He won re-election six times with at least 32 percentage points.[4] His retirement was confirmed on March 4, 2010, by the Boston Globe.[5] Shortly before the announcement of his retirement, it was discovered that Delahunt, while serving as district attorney for Norfolk County, Massachusetts, had refused to file charges against Amy Bishop for shooting and killing her brother in 1986. On February 12, 2010, Bishop murdered three of her colleagues at the University of Alabama in Huntsville after being denied tenure.

As one of his first initiatives in Congress, he created the bipartisan caucus on the United States Coast Guard, which he co-chaired with two other Coast Guard veterans, Reps. Howard Coble (R-NC) and Gene Taylor (D-MS). This benefited his district through getting the problems of outpaced resources and security recognized at the ports of Massachusetts.

In November 2005, he met with Venezuelan President Hugo Chavez to arrange an assistance program in which Venezuela would supply winter home heating oil at a 40 percent price reduction to thousands of low-income Massachusetts residents. The program, which has since been expanded to help 500,000 people across the U.S.,[6] was carried out via the Venezuelan owned Citgo, and brought accusations that Delahunt was assisting an anti-American leader. Delahunt, however, has sometimes criticized Chavez, such as in a September 2006 letter expressing "profound disgust" at a speech given by Chavez to the United Nations, in which he personally attacked PresidentGeorge W. Bush. In the letter he urged that Chavez express disagreements "in a more constructive manner."

Delahunt on retirement formed the Delahunt Group,[9] a lobbying firm ("multi-service consulting firm focused on Government Affairs, International Market Entry Strategies, Corporate and Development Advisory, Federal and State Funding, and Appropriations, Regulatory and Permitting Assistance, Public Policy Strategies and Public Relations"). Delahunt told the Cape Cod Times that he viewed it as an extension of his work in Congress. As a legislator, he explained, he set policy at a macro level. Now, he said: "we're taking that and bringing it down here to the communities, to encourage implementation. We're working with the private sector and the public sector in a way that's a win-win for everyone." He told the Times he is particularly interested in work that encourages regional tourism and economic development."[10]

Less than two months after leaving Congress, Delahunt lobbied on behalf of the Wampanoag people in Massachusetts to help them secure Indian gaming rights with the state legislature. Delahunt filled a gap left by the Wampanoag's previous lobbyist Jack Abramoff following his conviction associated with the renowned Jack Abramoff Indian lobbying scandal. Delahunt received over $15,000 in campaign contributions from the Wampanoag and Abramoff prior to leaving office sparking criticisms from good government advocates and casino opponents. While Delahunt is precluded by law from lobbying the Congress for at least one year, rules do not preclude him from lobbying state legislatures.[11] Delahunt formally announced his retirement from Congress in March 2010, between March and December 2010 he made over $10,000 in campaign contributions to Massachusetts state legislators from his federal congressional PAC - a 500 percent increase from previous years' contributions.[12]

Delahunt has also established a lobbying partnership with the Washington, DC-based Prime Policy Group on ways American companies can establish themselves in foreign countries while helping foreign businesses with connections to in United States markets.[13] Prime Policy Group's clients include companies like Accenture,[14] which have been criticized for moving offshore to avoid paying U.S. taxes. This partnership dove tales with Delahunt's work on behalf of the Wampanoag as their primary backers are the Malaysian gambling giant Genting Group. Genting is seeking to establish a foothold in the United States with ventures in New York, Miami and Massachusetts. The Wampanoag venture, if approved, would give Genting a tax-free foot hold in Indian gaming in the United States.[15]

Delahunt, the President of Medical Marijuana of Massachusetts Inc.,[16] has applied for three medical marijuana dispensary licenses from the Massachusetts state Department of Public Health. The businesses would be located in Mashpee, Plymouth and Taunton. The locations would all be in separate counties, so they will not compete with each other in the selection process.[17]

Delahunt supports the creation of medical marijuana dispensaries to thwart the rise in prescription drug abuse. He will also be significantly involved in the operations of any of the dispensaries that Medical Marijuana of Massachusetts opens.[17]

Delahunt's paternal grandfather immigrated to the United States from Canada and his paternal grandmother's family was Irish.[18] He and his wife, Katharina E. Delahunt, divorced in 1986. They have one daughter, Kristin, and adopted another, Kara Mai (née Nguyen Mai Tai Trang), from Vietnam in 1975. While Congress was in session, Delahunt lived in a rented house with fellow Democratic politicians George Miller, Chuck Schumer, and Richard Durbin.[19]